December 22, 2007

Y chromosomes and mtDNA in African farmers and hunter-gatherers

Contrasting Signatures of Population Growth for Mitochondrial DNA and Y Chromosomes among Human Populations in Africa

Maya Metni Pilkington et al.

A history of Pleistocene population expansion has been inferredfrom the frequency spectrum of polymorphism in the mitochondrialDNA (mtDNA) of many human populations. Similar patterns arenot typically observed for autosomal and X-linked loci. Oneexplanation for this discrepancy is a recent population bottleneck,with different rates of recovery for haploid and autosomal locias a result of their different effective population sizes. Thishypothesis predicts that mitochondrial and Y chromosomal DNAwill show a similar skew in the frequency spectrum in populationsthat have experienced a recent increase in effective populationsize. We test this hypothesis by re-sequencing 6.6 kb of non-codingY chromosomal DNA and 780 basepairs of the mtDNA cytochromec oxidase subunit III (COIII) gene in 172 males from five Africanpopulations. Four tests of population expansion are employedfor each locus in each population: Fu's Fs statistic, the R2statistic, coalescent simulations and the mismatch distribution.Consistent with previous results, patterns of mtDNA polymorphismbetter fit a model of constant population size for food-gatheringpopulations and a model of population expansion for food-producingpopulations. In contrast, none of the tests reveal evidenceof Y chromosome growth for either food-gatherers or food-producers.The distinct mtDNA and Y chromosome polymorphism patterns mostlikely reflect sex-biased demographic processes in the recenthistory of African populations. We hypothesize that males experiencedsmaller effective population sizes and/or lower rates of migrationduring the Bantu expansion, which occurred over the last fivethousand years.

Old Blog Archive

Dienekes' Anthropology blog is dedicated to human population genetics, physical anthropology, archaeology, and history.

You are free to reuse any of the materials of this blog for non-commercial purposes, as long as you attribute them to Dienekes Pontikos and provide a link to either the individual blog entry or to Dienekes Anthropology Blog.

Feel free to send e-mail to Dienekes Pontikos, or follow @dienekesp on Twitter.